Anti-tarnish composition for coppercontaining surfaces



I V W 1:. am "m agents or surfactants, Eckeners or VlSCS m/Z' S L/ A 3,248,235 ANTI-TARNISH COMPOSITION FOR COPPER- CONTAINING SURFACES Donald M. Pryor and Louis F. Cason, both of St. Paul,

Minn., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware No Drawing. Filed Sept. 28, 1961, Ser. No. 141,292

6 Claims. (Cl. 106-3) This invention relates to an anti-tarnish composition for treating tarnished copper-containing surfaces and to a method for rendering such surfaces tarnish resistant.

Copper-containing surfaces, including copper alloys such as bronze, brass, etc., are notoriously susceptible to discoloration due to tarnishing of the copper. A great variety of copper cleaners have been suggested for the removal of tarnish deposits, e.g. copper oxides and sulfides. However, the problem of inhibiting the tarnishing of the cleaned copper-containing surface through the use of di- A further object is to provide a composition which simultaneously cleans copper-containing surfaces and renders such surfaces tarnish resistant for prolonged periods of time.

Yet another object is to provide a process for both cleaning and rendering copper-containing surfaces tarnish resist-ant.

Other objects and advantages will become apparent from the following description.

In accordance with this invention, a highly eflicient composition -for cleaning copper-containing surfaces and for rendering such surfaces tarnish resistant over an extended period of time comprises an aliphatic mercaptan of the formula C H SH wherein n is from 12 to 25,

preferably from 16 to 21, and at least one non-abrasive copper cleaning ingredient. If desired r als ma ed to the compo no u ing suspending k e. The adv a I 0 e 1 workers skilled in the art are considered to come within the contemplation of this invention.

In cleaning copper-containing surfaces various nonabrasive ingredients have been used to chemically remove mselves to United States Patent 0 3,248,235 Patented Apr. 26, 1966 the abrasive content of the formulation and provides significantly more effective tarnish resistance and a more efiicient utilization of the mercaptan compound.

It has now been found that aliphatic mercaptans of the above formula provide a thin, colorless, non-oily protective layer on clean copper-containing surfaces, bonding to the copper through the thiol grouping, and that such mercaptans may be incorporated into copper cleaning formulations to provide a protective layer on the copper substrate as the tarnish is effectively removed by the cleaning ingredients. The bond between the copper and the mercaptans is unusually strong, resisting washing with dilute alkaline or acid solutions, and with detergent solutions. of equal importance is the colorless, transparent protective layer of these mercaptan molecules, which does not adversely effect the luster of the copper-containing surface and which does not discolor or embrittle with aging. Moreover, although the film of mercaptan is virtually invisible to the naked eye, the presence of the protective layer may be detected by the hydrophobic or water repellent properties of the protected surface.

Both branched and straight chain aliphatic mercaptans may be employed, although the straight chain mercaptans 5 are preferred. Mercaptans having less than twelve carbon atoms are not as desirable because of their somewhat greater volatility and greater difficulty in formulating with other desired cleaning ingredients. Mercaptans having more than twenty-five carbon atoms are not as desirable because they are higher melting solids and are more difficult to formulate. In general, these mercaptans have a mild odor which, if desired, may be masked with a suitable odorizer. They are non-toxic, particularly when considering the extremely minute quantities that are retained on the copper surface. Illustrative of the preferred mercaptans are n-hexadecane-l-thiol, n-dodecane-l-thiol, noctadecane-l-thiol, n-beneicos-ane-l-thio (C H SH), etc.

Of the many non-abrasive copper cleaning ingredients which do not react with these mercaptans and which may be used in the anti tarnish compositions of this invention the acidic cleaners are preferred because of their high efiioiency. The various combinations of acidic ingredi ents suitable for cleaning copper-containing surfaces are well known. Generally, when using acidic cleaning ingredients in aqueous media, a pH of below about 2.5 is preferred. The combination of a weak acid, e.g., citric acid, sulfamic aci cl, etc., and an alka 1 meta a e, efgf, sodium chloride, potassium chloride, etc., is an effective non-abrasive tarnish remover. Hydrochloric acid also is also is an effective non-abrasive copper cleaner. Since the anti-tarnish composition must be essentially nonoxidative, stron-g oxidizing acids, such as nitric acid, should not be used. Suitable acids having a pH between 1 and 5, which are water soluble, stable non-oxidizing the tarnish forming compounds. Con'ventionaL copper acids which do not form water insoluble compounds with cleaners frequently contain mild orgz'ifiic'iicids, such" as ESTEZE oT'sulfamic acidf t'ogether with sodium chloride, various surfactants and abrasives. After dissolution of the tarnish deposits by the non-a5rasive copper cleaning in gredients, which are usually acidic, and dislodging im- 0 bedded tarnish by abrasive and/or surfactant action, if desired, the copper containing surfaces are extremely reactive in contact with the corroding environment. It is therefore preferable, for providing prolonged tarnish resistance, to accomplish the cleaning and the tarnish prevention simultaneously. Moreover, although abrasive containing mercaptan formulations effectively clean and condition the tarnished surface, the concentration or loading" of abrasive required to remove the tarnish deposits tends to remove the protective mercaptan film as it is formed. The presence of non-abrasive copper cleaning ingredients permits the elimination of, or a reduction in,'

copper, as shown in US. Patent 2,628,199, are preferred.

The non-abrasive copper cleaners not only remove oxides from the tarnished copper surface but also permit the simultaneous formation of the continuous transparent fihn of the mercaptan compound. As mentioned earlier, when abrasives alone are employed in conjunction with the mercaptans compounds, the abrading effect tends to remove or disrupt the continuity of the protective film. Although abrasives may desirably be used in addition to the non-abrasive copper cleaners, particularly when heavy sulfide tarnish deposits are encountered, they constitute less than about 20 weight percent of the formulation and are preferably mild abrasives. Among the abrasive materials are finely divided (including m sillcas), clays, d-iatomaceous earths, precipitated chalks, etc.

In addition, sinall quantities of surfactant, particularly the nonionic variety, are usually employed. Viscosity acidic media.

stick or as a paste. Fol-certain uses it may be desirable ta impre griat fabrics with these anti-tarnish compositions to provide a convenient applicator cloth. It is also possible to dispense these compositions from pressurized containers, e.g., aerosols, etc.

Although the mercaptan, or mixture of mereaptans, can be incorporated in varying amounts into the compositions of this invention, depending partly on the physical nature of the formulation, it has been found that mercaptan conoentration within the 0.5 to 25, preferably 0.5 to 10, weight percent range is particularly effective in formations containing a non-abrasive copper cleaner. Less than about 0.5 percent of mercaptan does not generally provide suflicient tarnish resistance.

In an aqueous liquid composition the most preferred formulations usually contain from about 1 to weight percent of mercaptan, 0.01% to 25% of a weak organic f acid, 0.01% to 25% of an alkali metal halide (e.g., alkali metal chlorides, etc.), 0.05% to 1% of a surfactant, 0 to of an abrasive, sufficient water to emulsify the mercaptan, and sutiicient acid stable thickeners to provide the desired viscosity.

The anti-tarnish composition may be applied to the copper-containing surface by spraying, dipping, roll coating, applicator cloth, etc. If an abrasive is included in the formulation, the copper surface is polished until the tarnish deposits are removed. When -no abrasive is used, suflioient contact time is allowed to permit the copper cleaner to loosen and/or remove the tarnish, preferably followed y bufiing or wiping to bring out the lustre of the coppe surface. The removal of all tarnish is essential to obtain the continuous protective film required for extended protection of the surface. In all instances it is usually preferable to rinse the treated surface with water to remove an residual non-abrasive o0 er cleaner and g firasives Ihe following examples Wlll illustrate he various preferred formulations, their use and effectiveness in preventing the tarnishing of copper-containing surfaces for prolonged periods.

Example I Test panels of copper and brass were degreased with trichloroethylene and polished with a commercial copper cleaner containing a non-abrasive copper cleaner, i.e., citric acid and sodium chloride, to remove all traces of tarnish. Immediately after cleaning (a water rinse is preferable), the dry copper-containing surfaces were sprayed with a one percent solution of n-octadecane-lthiol in petroleum ether and buffed with a soft cloth. The panels were then exposed to hydrogen sulfide at about 70% relative humidity along with cleaned uncoated control panels. A marked difference in tarnish rate was noticed, the deposits forming on the controls in less than 15 minutes and the coated panels remaining essentially tarnish free for several hours.

Example 11 The procedure of Example I was repeated using nheneicosane-l-thiol instead of n-ocadecane-l-thiol. After exposure to the hydrogen sulfide atmosphere, the control panels (both copper and brass) tarnished in less than 15 minutes, whereas the treated panels were essentially tarnish free for several hours.

4 Example III The following formulation was prepared, the percentages being by weight:

Percent Water 60 Colloidal alumina (AlOOH) 3 n-Octadecane-l-mercaptan l0 Citric acid 8 Sodium chloride 8 Abrasive (50% diatomaceous earth and 50% of 240 mesh silica) 10 Nonionic surfactant 1 The colloidal alumina thickener was dissolved in water and the temperature raised to C. After mixing the mercaptan and the nonion-ic surfactant and heating to 80 C., the mixture was added to the colloidal alumina solution with high speed mixing, forming a thick creamy emulsion. Once emulsification was complete, the citric acid and the abrasive were added with continued stirring until a homogeneous dispersion was obtained. Then upon adding the sodium chloride, immediate thickening to a. smooth viscous paste occurred.

Copper panels were treated with the above formulation using a soft cloth, followed by water rinsing and air drying. Untreated copper panels whch had been cleaned to remove tarnish were used as controls. After immersing both a treated and an untreated panel in a 1% aqueous solution of hydrogen sulfide, the untreated control was observed to tarnish after 5 seconds whereas tarnishing of the treated panel occurred only after about 2 hours. A similar comparative test using a salt bath (5% aqueous sodium chloride) resulted in tarnishing of the untreated control in 30 minutes and no visible tarnishing of the treated panel after two days. Still another comparative test was made by placing both treated and untreated panels in a high temperature (212 F.) oxidative (air) environment, resulting in tarnishing of the untreated control in 10 minutes and tarnishing of the treated panel only after 6 hours. In each of the foregoing comparative tests the time reported is the time required for visible signs of tarnish to appear.

Example IV Results similar to those in Example III are obtained with the following formulation:

Percent Water 76 Hydrochloric acid 2.5 Colloidal alumina 4 Abrasive 15 n-Octadecane-l-mercaptan 2.4 Nonionic surfactant 0.1

Example V Results similar to those in Example III are obtained with the following formulation:

Percent Colloidal alumina 2.5 n-Octadecane-l-mercaptan 2.4 Citric acid 12 Sodium chloride 12 Diatomaceous earth 15 Nonionic surfactant 1 Water 55 Example VI A composition for dip treatment of tarnished copper panels was prepared with the following ingredients:

Tarnished copper panels were immersed in the above formulation, agitation being used to stabilize the dispersion. Tarnish deposits were removed within a few seconds. The panels were then rinsed with water Excellent resistance to tarnishing over an extended period of time was noted.

As used herein, copper is used interchangeably with copper-containing and includes, besides copper, such copper-containing alloys as brass, bronze, etc. having significant quantities of copper therein.

Various other embodiments and modifications will be apparent to those skilled in the art from the foregoing disclosure without departing from the spirit and scope of this invention.

We claim:

1. An aqueous anti-tarnish composition for copper which consists essentially of 0.01% to 25% of a weak organic acid, 0.01% to 25% of an alkali metal halide, 0.05% to 1% of a surfactant, 0 to 20% of abrasive, and 1 to 15% of a mercaptan of the formula where n is an integer from 12 to 25, the pH of said composition being below about 2.5.

References Cited by the Examiner UNITED STATES PATENTS 3/1945 Barnum 1486.24 7/1958 Murphy 1486.24

OTHER REFERENCES Bennett et al., The Chemical Formulary, vol. I, pages 417-32, published by D. Van Nostrand Co., Inc., New York., 1933.

ALEXANDER H. BRODMERKEL, Primary Examiner.

JOSEPH REBOLD, MORRIS LIEBMAN, Examiners. 

1. AN AQEOUS ANTI-TARNISH COMPOSITION FOR COPPER WHICH CONSISTS ESSENTIALLY OF 0.01% TO 25% OF A WEAK ORGANIC ACID, 0.01% TO 25% OF AN ALKALI METAL HALIDE, 0.05% TO 1% OF A SURFACTANT, 0 TO 20% OF ABRASIVE, AND 1 TO 15% OF A MERCAPTAN OF THE FORMULA 